1. Technical Field
The present disclosure relates to a multiple input multiple output (MIMO) training method for a MIMO operation performed in a wireless communication system and a wireless device.
2. Description of the Related Art
A network using a license-free 60 GHz (millimeter wave) band has received a significant amount of attention in recent years. The wireless high definition (HD) technology that allows multi-gigabit wireless streaming of Hi-Vision audio, video, and data among consumer electronics, personal computers, or portable devices is a first industrial 60-GHz (millimeter wave) band standard. An example of other multi-gigabit wireless communication technologies that use 60-GHz band is the WiGig technology standardized by Institute of Electrical and Electronic Engineers (IEEE) as “IEEE 802.11ad” (refer to, for example, IEEE Std 802.11ad™-2012, December 2012).
Unlike other IEEE 802.11 technologies using a 2.4 GHz or 5 GHz band, the WiGig technology employs beam forming to perform directional transmission. In 60-GHz millimeter wave band, the signal wavelength is relatively short, as compared with a typical object size in a propagation environment. Accordingly, ray-like propagation having a plurality of discrete spatial signal paths is dominant. Thus, by directing the beam of each of a transmission antenna (hereinafter referred to as a “TX antenna”) and a reception antenna (hereinafter referred to as an “RX antenna”) to an excellent spatial signal path, the quality of the signal, such as a signal-to-noise ratio (SNR), may be significantly increased.
In the WiGig technology, to select a beam having the best signal quality (also referred to as a “sector”), a phased beam training protocol (also referred to as “antenna beam training”) for the transmitter or the receiver to sweep all the antenna beams (the sectors) is employed. In a phase called the sector level sweep phase, antenna beam training is coarsely performed. Subsequently, a phase, called the beam refinement protocol phase or beam tracking phase, is performed to provide the fine tuning of an antenna beam for more excellent signal quality.